The present invention is directed to compound archery bows, and more particularly to a so-called single-cam compound archery bow having a power let-off cam mounted on the end of only one of the bow limbs.
Compound archery bows typically are of the so-called dual-cam design, originated in U.S. Pat. No. 3,486,495. Bows of this type typically comprise a bow handle having limbs mounted on and extending from opposed ends of the handle. Power let-off cams are rotatably mounted on the free ends of the bow limbs and are interconnected by one or more cable sections including a draw string section. As the bow draw string is drawn away from the handle, draw force initially increases as the limbs are drawn together and the cams rotate to a power let-off point, and thereafter the leverage increases and the draw force decreases as the cams rotate further but with little additional limb flexure. This so-called compound action allows full bow draw to be maintained at lesser force without fatigue to the archer. A problem inherent in dual-cam bows of this type lies in the fact that the cams must be closely matched and synchronized with each other in order to insure straight-line (or substantially straight-line) travel of the nock point on the bow string, and the limbs must be closely balanced and evenly stressed as the string is drawn. Damage to or mismatching of the cams, mismatch or incorrect adjustment of the limbs, or stretching of the cable sections can cause loss of synchronization between the cams and uneven stressing of the limbs, resulting in less than optimum performance of the bow.
In order to overcome the aforementioned deficiencies of dual-cam bows, it has heretofore been proposed to provide a compound bow that has a single power let-off cam disposed at the end of one bow limb, and a control pulley or wheel disposed at the end of the opposing limb over which the bow string is trained. U.S. Pat. No. 5,505,185 discloses such a single-cam compound bow. A control cable cooperates with the power let-off cam and a control groove in the control wheel to maintain the desired relationship or timing between bow string take-up grooves in the control wheel and power cam. In this way, identical or substantially identical incremental bow string cable travel to and from the bow string take-up grooves is obtained, thereby yielding straight-line nock travel as the bow string cable is drawn and released. A power cable extends from the power cam to the opposing bow limb for flexing the bow limbs uniformly as the bow string is drawn, and for cooperating with the power cam to obtain the power let-off action that is characteristic of compound bows.
Although the single-cam compound bow disclosed in the noted copending application addresses and overcomes many problems theretofore extant in the art, further improvements remain desirable. In particular, the noted application does not disclose any means or technique for adjusting draw length of the bow. That is, the bow disclosed in the noted application obtains straight-line nock travel for a given bow draw length for which the power cam and the control wheel are designed. In order to change or adjust bow string draw length, the power cam and/or the control wheel must be changed to accommodate the new desired draw length while maintaining synchronous timing between the cam and wheel. In a commercial single-cam compound bow of a different design, accommodation is made for changing the bow string cable anchor point at the power let-off cam, and thereby changing the bow string draw length. However, since the cams and wheels are optimized for only a single draw length, changing the bow string anchor point inherently changes the path of nock travel as the bow is drawn and released, and consequently affects accuracy of the bow.
Another problem in single-cam compound bows heretofore proposed lies in the creation of a torque or twisting force on the bow limb that carries the power let-off cam, which varies as the bowstring is drawn and released. Bow limb torque is not a problem at the limb that carries the control wheel because the power cable segment can be anchored to the limb at both sides of the control wheel, and because the cable groove or grooves in the control wheel can be placed very close to the limb centerline. However, at the power cam, the bow string, power cable and control cable segments engage the cam at laterally spaced positions. These cable segments apply a torque through the cam axle to the bow limb. This problem is exacerbated when a cable guard is employed on the bow because the cable guard offsets the control and power cable segments from the bow limb centerline.
It is therefore a general object of the present invention to provide a compound bow that obtains the benefits of single-cam compound bow designs as compared with dual-cam designsxe2x80x94i.e., obtains uniform stressing of the bow limbs and straight-line (or substantially straight-line) nock travelxe2x80x94for a range of draw lengths. That is, an object of the present invention is to provide a single-cam compound bow in which the bow string draw length can be adjusted without deleteriously affecting other salutary operating characteristics of the bow. A more specific object of the present invention is to provide a single-cam compound bow of the described character in which bow string draw length can be adjusted by adjusting and/or replacing draw length modules on the bow power cam. A further and related object of the present invention is to provide a single-cam compound bow of the described character that obtains the foregoing objectives while employing standard cable lengths for economy of manufacture and service. Yet another object of the present invention is to provide a single-cam compound bow that has a positive bow string draw stop, which is deemed particularly desirable by archery enthusiasts, that automatically adjusts with draw length. A further object of the invention is to provide a single-cam compound bow in which torque applied to the power-cam limb, as the bow is drawn and released, is reduced or eliminated.
A single-cam compound archery bow in accordance with the present invention includes a bow handle with a pair of projecting limbs and a pair of cable pulleys rotatably mounted on the ends of the bow limbs. A bow cable includes a first cable segment anchored at one end to one of the bow limbs and at a second end to the opposing second pulley. Second and third cable segments are each anchored at one end to the second pulley and extend to the first pulley. The third cable segment has a nock point that, when drawn away from the handle, unwraps the third cable segment equally from the first and second pulleys, wraps the second cable segment onto the second pulley as the third cable segment is unwrapped therefrom, and wraps the first cable segment into a pulley groove in the first pulley so as to draw the limb ends together up to a power let-off point at the pulley groove. Length of the pulley groove, and consequently position of the power let-off point on the second pulley, is adjustable while maintaining a fixed spacing between the power let-off point and the anchor point of the second cable segment to the second pulley. In this way, the nock point travels in a straight line as the third cable segment is drawn away from the bow handle independent of length of the pulley groove between the power let-off point and the anchor of the first cable segment to the second pulley.
A single-cam compound archery bow in accordance with presently preferred embodiments of the invention includes a bow handle having spaced ends from which bow limbs project, a control wheel rotatably mounted on one end of one limb and a power cam rotatably mounted at an opposing end of the other limb. A power cable segment is anchored at one end to the one limb and at a second end to the power cam at a position to wrap into and unwrap from a power cable groove on the power cam. A bow string cable segment is anchored to the control wheel and to the power cam at positions to wrap into and unwrap from first and second bow string take-up grooves on the control wheel and power cam respectively. The bow string cable segment has a nock point disposed between the spaced limb ends. A control cable segment is anchored at one end to the control wheel at a position to wrap into and unwrap from a control groove on the control wheel, and is anchored at an opposing end to the power cam. As the bow string cable segment is drawn away from the handle, the bow string cable segment unwraps equally from the control wheel and the power cam, wraps the power cable segment into the power cable groove on the power cam so as to draw the bow limb ends together up to a power let-off point at the power cable groove, and wraps the control cable segment into the control groove on the control wheel. Length of the power cable groove on the power cam, and position of the power let-off point on the power cam, are adjustable while maintaining a fixed separation between the power let-off point and the control cable anchor on the power cam, so that the nock point travels in a straight line as the bow string cable segment is drawn and released independent of adjusted length of the power cable groove and position of the power let-off point.
In a single-cam compound archery bow in accordance with modified embodiments of the invention, the control wheel of the preferred embodiment is replaced by an idler pulley that has a single groove concentric with the axis of rotation. The control cable groove on the power cam is replaced by a second bowstring take-up groove. The bowstring is anchored at both ends to the power cam at positions to wrap into and unwrap from the first and second bowstring take-up grooves, and extends in a continuous run around the idler pulley. The continuous length of bowstring cable thus effectively forms a bowstring cable segment on what the nock is positioned, and a bowstring/control cable segment that is anchored to the power cam and controls play-out of the bowstring cable segment. Length of the power cable groove on the power cam, and position of the power let-off point on the power cam, are adjustable while maintaining a fixed separation between the power let-off point and the anchor point of the bowstring/control cable segment on the power cam. In this way, the nock point travels in a straight (or substantially straight) line as the bowstring cable segment is drawn and released independent of adjusted length of the power cable groove and position of the power let-off point.
In the preferred embodiments of the invention, the power cam comprises a cam base that includes the second bow string take-up groove, and a plurality of modules mountable on the base to provide power cable grooves of differing adjustable lengths. Each module is thus both selectively mountable/demountable on the cam base and adjustably positionable on the cam base for obtaining adjustable draw length over a wide draw length range. Each module has facility for affixing the anchor point of the control cable so as to maintain a fixed spacing between such anchor point and the associated power let-off point of each module. Thus, bow string draw length is adjustable over a wide range without in any way affecting other design capabilities of the bow, including particularly straight-line movement of the draw string nock point. In the preferred embodiment of the invention, the power cable segment, the control cable segment and the bow string cable segment are provided as separate lengths of cable stock, as distinguished from a continuous length of cable stock which is less preferred. In this way, the cable segments may be provided in standard lengths, which greatly facilitates economy of both manufacture and service. The bow power cam, specifically the adjustable/replaceable draw length module, includes a stop surface that circumferentially aligns with the power cable groove in the module, and which forms a positive stop against wrap of the power cable into the groove as the bow string is drawn. This feature of the invention provides a positive stop against bow string draw, which is particularly desired by archery enthusiasts. Furthermore, since the stop is provided on the adjustable module rather than the power cam base, stop position is automatically adjusted along with bow string draw length.
In accordance with another feature of the preferred embodiment of the invention, the control groove on the control wheel, into  arm of the cam from which the control cable wraps  unwraps as the bow string is drawn, is contoured to reduce twisting forces on the bow limb. Specifically, the control groove is contoured to reduce lateral separation between the control cable and the power cable as the power cable and control cable are  is wrapped into the power cam and the control cable is unwrapped (i.e., as the bow string cable is withdrawn). This reduced lateral spacing reduces the force differential on the power cam that tends to twist the bow limb in which the power cam is mounted.